August 26 – Battle of Manzikert: The Byzantine army (35,000 men) under Emperor Romanos IV meets the Seljuk Turk forces of Sultan Alp Arslan near the town of Manzikert. Although the armies are initially evenly matched, as the Byzantines advance, the Seljuk Turks withdraw before them, launching hit-and-run attacks on the Byzantine flanks. While attempting to withdraw, the Byzantine army falls apart, either through treachery or confusion; the battle ends in a decisive defeat for the Byzantine Empire. Romanos is captured (though released by Alp Arslan within a week) and much of the elite Varangian Guard is destroyed; this will prove catastrophic for the Byzantine Empire.
Edwin, earl of Mercia, rebels against William I, but is betrayed and killed. His castle and lands at Dudley (located in the West Midlands) are given to William's Norman subjects.